Noninterventional Study Evaluating Parkinson's Disease Diary Use

Inclusion Criteria * ≥39 to ≤70 years of age at signing of informed consent * Diagnosis of clinically established PD as defined by the Movement Disorder Society (MDS) Clinical Diagnostic Criteria for PD * Marked levodopa responsiveness at screening per investigator's judgment (eg, an estimated ≥30% improvement of MDS-UPDRS Part III score in the off-medication versus on-medication state) * A minimum of 3 years and a maximum of 10 years from time of PD diagnosis to the date of screening * Receiving optimized and stable PD medical therapy for ≥1 month prior to screening or demonstrated intolerance to PD medications per investigator's judgment in agreement with the medical monitor * ≥2 hours of average daily OFF-time assessed within 3 months of screening by PD diary or per investigator's judgment * Hoehn and Yahr Stage of 1 to 3 while on PD medication assessed within 3 months of screening or at screening * Normal cognition as determined by the investigator after review of relevant testing (eg, Montreal Cognitive Assessment score of ≥26, or ≥22 if no significant cognitive impairment as determined by neuropsychological testing) Exclusion Criteria: * PD with risk of recurrent falls or only tremor-based symptoms * Diagnosis of primary mitochondrial disorder, epilepsy, stroke, multiple sclerosis, or clinical features suggestive of a neurodegenerative disease other than PD such as Alzheimer's disease * Any available evidence inconsistent with dopamine deficiency (eg, 18F-DOPA positron emission tomography \[PET\] or dopamine transporter single-photon emission computed tomography \[DAT-SPECT\] imaging if performed) * Moderately severe dyskinesia per investigator's judgment * Receiving dopamine receptor-blocking agents, including typical neuroleptics, prochlorperazine, and metoclopramide at the time of screening or within 3 months prior to screening * Treatment with intrajejunal or subcutaneous infusion therapies for PD within 2 months of screening * History of gene therapy or cell therapy * Prior surgical or radiation therapy to the brain, including deep brain stimulation and lesion therapy, or prior history of intradural spinal cord surgery * Receipt of another investigational therapy or device within 2 years of screening unless approved by the medical monitor